// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
 */

#include <string.h>
#include <stdlib.h>

#include "builtin.h"
#include "cfi.h"
#include "arch.h"
#include "check.h"
#include "special.h"
#include "warn.h"
#include "arch_elf.h"

#include <linux/hashtable.h>
#include <linux/kernel.h>

#define FAKE_JUMP_OFFSET -1

#define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"

struct alternative {
        struct list_head list;
        struct instruction *insn;
        bool skip_orig;
};

const char *objname;
struct cfi_init_state initial_func_cfi;

struct instruction *find_insn(struct objtool_file *file,
                              struct section *sec, unsigned long offset)
{
        struct instruction *insn;

        hash_for_each_possible(file->insn_hash, insn, hash, sec_offset_hash(sec, offset)) {
                if (insn->sec == sec && insn->offset == offset)
                        return insn;
        }

        return NULL;
}

static struct instruction *next_insn_same_sec(struct objtool_file *file,
                                              struct instruction *insn)
{
        struct instruction *next = list_next_entry(insn, list);

        if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
                return NULL;

        return next;
}

static struct instruction *next_insn_same_func(struct objtool_file *file,
                                               struct instruction *insn)
{
        struct instruction *next = list_next_entry(insn, list);
        struct symbol *func = insn->func;

        if (!func)
                return NULL;

        if (&next->list != &file->insn_list && next->func == func)
                return next;

        /* Check if we're already in the subfunction: */
        if (func == func->cfunc)
                return NULL;

        /* Move to the subfunction: */
        return find_insn(file, func->cfunc->sec, func->cfunc->offset);
}

static struct instruction *prev_insn_same_sym(struct objtool_file *file,
                                               struct instruction *insn)
{
        struct instruction *prev = list_prev_entry(insn, list);

        if (&prev->list != &file->insn_list && prev->func == insn->func)
                return prev;

        return NULL;
}

#define func_for_each_insn(file, func, insn)                            \
        for (insn = find_insn(file, func->sec, func->offset);           \
             insn;                                                      \
             insn = next_insn_same_func(file, insn))

#define sym_for_each_insn(file, sym, insn)                              \
        for (insn = find_insn(file, sym->sec, sym->offset);             \
             insn && &insn->list != &file->insn_list &&                 \
                insn->sec == sym->sec &&                                \
                insn->offset < sym->offset + sym->len;                  \
             insn = list_next_entry(insn, list))

#define sym_for_each_insn_continue_reverse(file, sym, insn)             \
        for (insn = list_prev_entry(insn, list);                        \
             &insn->list != &file->insn_list &&                         \
                insn->sec == sym->sec && insn->offset >= sym->offset;   \
             insn = list_prev_entry(insn, list))

#define sec_for_each_insn_from(file, insn)                              \
        for (; insn; insn = next_insn_same_sec(file, insn))

#define sec_for_each_insn_continue(file, insn)                          \
        for (insn = next_insn_same_sec(file, insn); insn;               \
             insn = next_insn_same_sec(file, insn))

static bool is_static_jump(struct instruction *insn)
{
        return insn->type == INSN_JUMP_CONDITIONAL ||
               insn->type == INSN_JUMP_UNCONDITIONAL;
}

static bool is_sibling_call(struct instruction *insn)
{
        /* An indirect jump is either a sibling call or a jump to a table. */
        if (insn->type == INSN_JUMP_DYNAMIC)
                return list_empty(&insn->alts);

        if (!is_static_jump(insn))
                return false;

        /* add_jump_destinations() sets insn->call_dest for sibling calls. */
        return !!insn->call_dest;
}

/*
 * This checks to see if the given function is a "noreturn" function.
 *
 * For global functions which are outside the scope of this object file, we
 * have to keep a manual list of them.
 *
 * For local functions, we have to detect them manually by simply looking for
 * the lack of a return instruction.
 */
static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
                                int recursion)
{
        int i;
        struct instruction *insn;
        bool empty = true;

        /*
         * Unfortunately these have to be hard coded because the noreturn
         * attribute isn't provided in ELF data.
         */
        static const char * const global_noreturns[] = {
                "__stack_chk_fail",
                "panic",
                "do_exit",
                "do_task_dead",
                "__module_put_and_exit",
                "complete_and_exit",
                "__reiserfs_panic",
                "lbug_with_loc",
                "fortify_panic",
                "usercopy_abort",
                "machine_real_restart",
                "rewind_stack_do_exit",
                "kunit_try_catch_throw",
        };

        if (!func)
                return false;

        if (func->bind == STB_WEAK)
                return false;

        if (func->bind == STB_GLOBAL)
                for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
                        if (!strcmp(func->name, global_noreturns[i]))
                                return true;

        if (!func->len)
                return false;

        insn = find_insn(file, func->sec, func->offset);
        if (!insn->func)
                return false;

        func_for_each_insn(file, func, insn) {
                empty = false;

                if (insn->type == INSN_RETURN)
                        return false;
        }

        if (empty)
                return false;

        /*
         * A function can have a sibling call instead of a return.  In that
         * case, the function's dead-end status depends on whether the target
         * of the sibling call returns.
         */
        func_for_each_insn(file, func, insn) {
                if (is_sibling_call(insn)) {
                        struct instruction *dest = insn->jump_dest;

                        if (!dest)
                                /* sibling call to another file */
                                return false;

                        /* local sibling call */
                        if (recursion == 5) {
                                /*
                                 * Infinite recursion: two functions have
                                 * sibling calls to each other.  This is a very
                                 * rare case.  It means they aren't dead ends.
                                 */
                                return false;
                        }

                        return __dead_end_function(file, dest->func, recursion+1);
                }
        }

        return true;
}

static bool dead_end_function(struct objtool_file *file, struct symbol *func)
{
        return __dead_end_function(file, func, 0);
}

static void init_cfi_state(struct cfi_state *cfi)
{
        int i;

        for (i = 0; i < CFI_NUM_REGS; i++) {
                cfi->regs[i].base = CFI_UNDEFINED;
                cfi->vals[i].base = CFI_UNDEFINED;
        }
        cfi->cfa.base = CFI_UNDEFINED;
        cfi->drap_reg = CFI_UNDEFINED;
        cfi->drap_offset = -1;
}

static void init_insn_state(struct insn_state *state, struct section *sec)
{
        memset(state, 0, sizeof(*state));
        init_cfi_state(&state->cfi);

        /*
         * We need the full vmlinux for noinstr validation, otherwise we can
         * not correctly determine insn->call_dest->sec (external symbols do
         * not have a section).
         */
        if (vmlinux && sec)
                state->noinstr = sec->noinstr;
}

/*
 * Call the arch-specific instruction decoder for all the instructions and add
 * them to the global instruction list.
 */
static int decode_instructions(struct objtool_file *file)
{
        struct section *sec;
        struct symbol *func;
        unsigned long offset;
        struct instruction *insn;
        unsigned long nr_insns = 0;
        int ret;

        for_each_sec(file, sec) {

                if (!(sec->sh.sh_flags & SHF_EXECINSTR))
                        continue;

                if (strcmp(sec->name, ".altinstr_replacement") &&
                    strcmp(sec->name, ".altinstr_aux") &&
                    strncmp(sec->name, ".discard.", 9))
                        sec->text = true;

                if (!strcmp(sec->name, ".noinstr.text") ||
                    !strcmp(sec->name, ".entry.text"))
                        sec->noinstr = true;

                for (offset = 0; offset < sec->len; offset += insn->len) {
                        insn = malloc(sizeof(*insn));
                        if (!insn) {
                                WARN("malloc failed");
                                return -1;
                        }
                        memset(insn, 0, sizeof(*insn));
                        INIT_LIST_HEAD(&insn->alts);
                        INIT_LIST_HEAD(&insn->stack_ops);
                        init_cfi_state(&insn->cfi);

                        insn->sec = sec;
                        insn->offset = offset;

                        ret = arch_decode_instruction(file->elf, sec, offset,
                                                      sec->len - offset,
                                                      &insn->len, &insn->type,
                                                      &insn->immediate,
                                                      &insn->stack_ops);
                        if (ret)
                                goto err;

                        hash_add(file->insn_hash, &insn->hash, sec_offset_hash(sec, insn->offset));
                        list_add_tail(&insn->list, &file->insn_list);
                        nr_insns++;
                }

                list_for_each_entry(func, &sec->symbol_list, list) {
                        if (func->type != STT_FUNC || func->alias != func)
                                continue;

                        if (!find_insn(file, sec, func->offset)) {
                                WARN("%s(): can't find starting instruction",
                                     func->name);
                                return -1;
                        }

                        sym_for_each_insn(file, func, insn)
                                insn->func = func;
                }
        }

        if (stats)
                printf("nr_insns: %lu\n", nr_insns);

        return 0;

err:
        free(insn);
        return ret;
}

static struct instruction *find_last_insn(struct objtool_file *file,
                                          struct section *sec)
{
        struct instruction *insn = NULL;
        unsigned int offset;
        unsigned int end = (sec->len > 10) ? sec->len - 10 : 0;

        for (offset = sec->len - 1; offset >= end && !insn; offset--)
                insn = find_insn(file, sec, offset);

        return insn;
}

/*
 * Mark "ud2" instructions and manually annotated dead ends.
 */
static int add_dead_ends(struct objtool_file *file)
{
        struct section *sec;
        struct reloc *reloc;
        struct instruction *insn;

        /*
         * By default, "ud2" is a dead end unless otherwise annotated, because
         * GCC 7 inserts it for certain divide-by-zero cases.
         */
        for_each_insn(file, insn)
                if (insn->type == INSN_BUG)
                        insn->dead_end = true;

        /*
         * Check for manually annotated dead ends.
         */
        sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
        if (!sec)
                goto reachable;

        list_for_each_entry(reloc, &sec->reloc_list, list) {
                if (reloc->sym->type != STT_SECTION) {
                        WARN("unexpected relocation symbol type in %s", sec->name);
                        return -1;
                }
                insn = find_insn(file, reloc->sym->sec, reloc->addend);
                if (insn)
                        insn = list_prev_entry(insn, list);
                else if (reloc->addend == reloc->sym->sec->len) {
                        insn = find_last_insn(file, reloc->sym->sec);
                        if (!insn) {
                                WARN("can't find unreachable insn at %s+0x%x",
                                     reloc->sym->sec->name, reloc->addend);
                                return -1;
                        }
                } else {
                        WARN("can't find unreachable insn at %s+0x%x",
                             reloc->sym->sec->name, reloc->addend);
                        return -1;
                }

                insn->dead_end = true;
        }

reachable:
        /*
         * These manually annotated reachable checks are needed for GCC 4.4,
         * where the Linux unreachable() macro isn't supported.  In that case
         * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
         * not a dead end.
         */
        sec = find_section_by_name(file->elf, ".rela.discard.reachable");
        if (!sec)
                return 0;

        list_for_each_entry(reloc, &sec->reloc_list, list) {
                if (reloc->sym->type != STT_SECTION) {
                        WARN("unexpected relocation symbol type in %s", sec->name);
                        return -1;
                }
                insn = find_insn(file, reloc->sym->sec, reloc->addend);
                if (insn)
                        insn = list_prev_entry(insn, list);
                else if (reloc->addend == reloc->sym->sec->len) {
                        insn = find_last_insn(file, reloc->sym->sec);
                        if (!insn) {
                                WARN("can't find reachable insn at %s+0x%x",
                                     reloc->sym->sec->name, reloc->addend);
                                return -1;
                        }
                } else {
                        WARN("can't find reachable insn at %s+0x%x",
                             reloc->sym->sec->name, reloc->addend);
                        return -1;
                }

                insn->dead_end = false;
        }

        return 0;
}

/*
 * Warnings shouldn't be reported for ignored functions.
 */
static void add_ignores(struct objtool_file *file)
{
        struct instruction *insn;
        struct section *sec;
        struct symbol *func;
        struct reloc *reloc;

        sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
        if (!sec)
                return;

        list_for_each_entry(reloc, &sec->reloc_list, list) {
                switch (reloc->sym->type) {
                case STT_FUNC:
                        func = reloc->sym;
                        break;

                case STT_SECTION:
                        func = find_func_by_offset(reloc->sym->sec, reloc->addend);
                        if (!func)
                                continue;
                        break;

                default:
                        WARN("unexpected relocation symbol type in %s: %d", sec->name, reloc->sym->type);
                        continue;
                }

                func_for_each_insn(file, func, insn)
                        insn->ignore = true;
        }
}

/*
 * This is a whitelist of functions that is allowed to be called with AC set.
 * The list is meant to be minimal and only contains compiler instrumentation
 * ABI and a few functions used to implement *_{to,from}_user() functions.
 *
 * These functions must not directly change AC, but may PUSHF/POPF.
 */
static const char *uaccess_safe_builtin[] = {
        /* KASAN */
        "kasan_report",
        "check_memory_region",
        /* KASAN out-of-line */
        "__asan_loadN_noabort",
        "__asan_load1_noabort",
        "__asan_load2_noabort",
        "__asan_load4_noabort",
        "__asan_load8_noabort",
        "__asan_load16_noabort",
        "__asan_storeN_noabort",
        "__asan_store1_noabort",
        "__asan_store2_noabort",
        "__asan_store4_noabort",
        "__asan_store8_noabort",
        "__asan_store16_noabort",
        /* KASAN in-line */
        "__asan_report_load_n_noabort",
        "__asan_report_load1_noabort",
        "__asan_report_load2_noabort",
        "__asan_report_load4_noabort",
        "__asan_report_load8_noabort",
        "__asan_report_load16_noabort",
        "__asan_report_store_n_noabort",
        "__asan_report_store1_noabort",
        "__asan_report_store2_noabort",
        "__asan_report_store4_noabort",
        "__asan_report_store8_noabort",
        "__asan_report_store16_noabort",
        /* KCSAN */
        "__kcsan_check_access",
        "kcsan_found_watchpoint",
        "kcsan_setup_watchpoint",
        "kcsan_check_scoped_accesses",
        "kcsan_disable_current",
        "kcsan_enable_current_nowarn",
        /* KCSAN/TSAN */
        "__tsan_func_entry",
        "__tsan_func_exit",
        "__tsan_read_range",
        "__tsan_write_range",
        "__tsan_read1",
        "__tsan_read2",
        "__tsan_read4",
        "__tsan_read8",
        "__tsan_read16",
        "__tsan_write1",
        "__tsan_write2",
        "__tsan_write4",
        "__tsan_write8",
        "__tsan_write16",
        /* KCOV */
        "write_comp_data",
        "check_kcov_mode",
        "__sanitizer_cov_trace_pc",
        "__sanitizer_cov_trace_const_cmp1",
        "__sanitizer_cov_trace_const_cmp2",
        "__sanitizer_cov_trace_const_cmp4",
        "__sanitizer_cov_trace_const_cmp8",
        "__sanitizer_cov_trace_cmp1",
        "__sanitizer_cov_trace_cmp2",
        "__sanitizer_cov_trace_cmp4",
        "__sanitizer_cov_trace_cmp8",
        "__sanitizer_cov_trace_switch",
        /* UBSAN */
        "ubsan_type_mismatch_common",
        "__ubsan_handle_type_mismatch",
        "__ubsan_handle_type_mismatch_v1",
        "__ubsan_handle_shift_out_of_bounds",
        /* misc */
        "csum_partial_copy_generic",
        "__memcpy_mcsafe",
        "mcsafe_handle_tail",
        "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
        NULL
};

static void add_uaccess_safe(struct objtool_file *file)
{
        struct symbol *func;
        const char **name;

        if (!uaccess)
                return;

        for (name = uaccess_safe_builtin; *name; name++) {
                func = find_symbol_by_name(file->elf, *name);
                if (!func)
                        continue;

                func->uaccess_safe = true;
        }
}

/*
 * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 * But it at least allows objtool to understand the control flow *around* the
 * retpoline.
 */
static int add_ignore_alternatives(struct objtool_file *file)
{
        struct section *sec;
        struct reloc *reloc;
        struct instruction *insn;

        sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
        if (!sec)
                return 0;

        list_for_each_entry(reloc, &sec->reloc_list, list) {
                if (reloc->sym->type != STT_SECTION) {
                        WARN("unexpected relocation symbol type in %s", sec->name);
                        return -1;
                }

                insn = find_insn(file, reloc->sym->sec, reloc->addend);
                if (!insn) {
                        WARN("bad .discard.ignore_alts entry");
                        return -1;
                }

                insn->ignore_alts = true;
        }

        return 0;
}

/*
 * Find the destination instructions for all jumps.
 */
static int add_jump_destinations(struct objtool_file *file)
{
        struct instruction *insn;
        struct reloc *reloc;
        struct section *dest_sec;
        unsigned long dest_off;

        for_each_insn(file, insn) {
                if (!is_static_jump(insn))
                        continue;

                if (insn->offset == FAKE_JUMP_OFFSET)
                        continue;

                reloc = find_reloc_by_dest_range(file->elf, insn->sec,
                                               insn->offset, insn->len);
                if (!reloc) {
                        dest_sec = insn->sec;
                        dest_off = arch_jump_destination(insn);
                } else if (reloc->sym->type == STT_SECTION) {
                        dest_sec = reloc->sym->sec;
                        dest_off = arch_dest_reloc_offset(reloc->addend);
                } else if (reloc->sym->sec->idx) {
                        dest_sec = reloc->sym->sec;
                        dest_off = reloc->sym->sym.st_value +
                                   arch_dest_reloc_offset(reloc->addend);
                } else if (strstr(reloc->sym->name, "_indirect_thunk_")) {
                        /*
                         * Retpoline jumps are really dynamic jumps in
                         * disguise, so convert them accordingly.
                         */
                        if (insn->type == INSN_JUMP_UNCONDITIONAL)
                                insn->type = INSN_JUMP_DYNAMIC;
                        else
                                insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;

                        insn->retpoline_safe = true;
                        continue;
                } else {
                        /* external sibling call */
                        insn->call_dest = reloc->sym;
                        continue;
                }

                insn->jump_dest = find_insn(file, dest_sec, dest_off);
                if (!insn->jump_dest) {

                        /*
                         * This is a special case where an alt instruction
                         * jumps past the end of the section.  These are
                         * handled later in handle_group_alt().
                         */
                        if (!strcmp(insn->sec->name, ".altinstr_replacement"))
                                continue;

                        WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
                                  insn->sec, insn->offset, dest_sec->name,
                                  dest_off);
                        return -1;
                }

                /*
                 * Cross-function jump.
                 */
                if (insn->func && insn->jump_dest->func &&
                    insn->func != insn->jump_dest->func) {

                        /*
                         * For GCC 8+, create parent/child links for any cold
                         * subfunctions.  This is _mostly_ redundant with a
                         * similar initialization in read_symbols().
                         *
                         * If a function has aliases, we want the *first* such
                         * function in the symbol table to be the subfunction's
                         * parent.  In that case we overwrite the
                         * initialization done in read_symbols().
                         *
                         * However this code can't completely replace the
                         * read_symbols() code because this doesn't detect the
                         * case where the parent function's only reference to a
                         * subfunction is through a jump table.
                         */
                        if (!strstr(insn->func->name, ".cold.") &&
                            strstr(insn->jump_dest->func->name, ".cold.")) {
                                insn->func->cfunc = insn->jump_dest->func;
                                insn->jump_dest->func->pfunc = insn->func;

                        } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
                                   insn->jump_dest->offset == insn->jump_dest->func->offset) {

                                /* internal sibling call */
                                insn->call_dest = insn->jump_dest->func;
                        }
                }
        }

        return 0;
}

static void remove_insn_ops(struct instruction *insn)
{
        struct stack_op *op, *tmp;

        list_for_each_entry_safe(op, tmp, &insn->stack_ops, list) {
                list_del(&op->list);
                free(op);
        }
}

/*
 * Find the destination instructions for all calls.
 */
static int add_call_destinations(struct objtool_file *file)
{
        struct instruction *insn;
        unsigned long dest_off;
        struct reloc *reloc;

        for_each_insn(file, insn) {
                if (insn->type != INSN_CALL)
                        continue;

                reloc = find_reloc_by_dest_range(file->elf, insn->sec,
                                               insn->offset, insn->len);
                if (!reloc) {
                        dest_off = arch_jump_destination(insn);
                        insn->call_dest = find_func_by_offset(insn->sec, dest_off);
                        if (!insn->call_dest)
                                insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);

                        if (insn->ignore)
                                continue;

                        if (!insn->call_dest) {
                                WARN_FUNC("unannotated intra-function call", insn->sec, insn->offset);
                                return -1;
                        }

                        if (insn->func && insn->call_dest->type != STT_FUNC) {
                                WARN_FUNC("unsupported call to non-function",
                                          insn->sec, insn->offset);
                                return -1;
                        }

                } else if (reloc->sym->type == STT_SECTION) {
                        dest_off = arch_dest_reloc_offset(reloc->addend);
                        insn->call_dest = find_func_by_offset(reloc->sym->sec,
                                                              dest_off);
                        if (!insn->call_dest) {
                                WARN_FUNC("can't find call dest symbol at %s+0x%lx",
                                          insn->sec, insn->offset,
                                          reloc->sym->sec->name,
                                          dest_off);
                                return -1;
                        }
                } else
                        insn->call_dest = reloc->sym;

                /*
                 * Many compilers cannot disable KCOV with a function attribute
                 * so they need a little help, NOP out any KCOV calls from noinstr
                 * text.
                 */
                if (insn->sec->noinstr &&
                    !strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
                        if (reloc) {
                                reloc->type = R_NONE;
                                elf_write_reloc(file->elf, reloc);
                        }

                        elf_write_insn(file->elf, insn->sec,
                                       insn->offset, insn->len,
                                       arch_nop_insn(insn->len));
                        insn->type = INSN_NOP;
                }

                /*
                 * Whatever stack impact regular CALLs have, should be undone
                 * by the RETURN of the called function.
                 *
                 * Annotated intra-function calls retain the stack_ops but
                 * are converted to JUMP, see read_intra_function_calls().
                 */
                remove_insn_ops(insn);
        }

        return 0;
}

/*
 * The .alternatives section requires some extra special care, over and above
 * what other special sections require:
 *
 * 1. Because alternatives are patched in-place, we need to insert a fake jump
 *    instruction at the end so that validate_branch() skips all the original
 *    replaced instructions when validating the new instruction path.
 *
 * 2. An added wrinkle is that the new instruction length might be zero.  In
 *    that case the old instructions are replaced with noops.  We simulate that
 *    by creating a fake jump as the only new instruction.
 *
 * 3. In some cases, the alternative section includes an instruction which
 *    conditionally jumps to the _end_ of the entry.  We have to modify these
 *    jumps' destinations to point back to .text rather than the end of the
 *    entry in .altinstr_replacement.
 */
static int handle_group_alt(struct objtool_file *file,
                            struct special_alt *special_alt,
                            struct instruction *orig_insn,
                            struct instruction **new_insn)
{
        static unsigned int alt_group_next_index = 1;
        struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
        unsigned int alt_group = alt_group_next_index++;
        unsigned long dest_off;

        last_orig_insn = NULL;
        insn = orig_insn;
        sec_for_each_insn_from(file, insn) {
                if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
                        break;

                insn->alt_group = alt_group;
                last_orig_insn = insn;
        }

        if (next_insn_same_sec(file, last_orig_insn)) {
                fake_jump = malloc(sizeof(*fake_jump));
                if (!fake_jump) {
                        WARN("malloc failed");
                        return -1;
                }
                memset(fake_jump, 0, sizeof(*fake_jump));
                INIT_LIST_HEAD(&fake_jump->alts);
                INIT_LIST_HEAD(&fake_jump->stack_ops);
                init_cfi_state(&fake_jump->cfi);

                fake_jump->sec = special_alt->new_sec;
                fake_jump->offset = FAKE_JUMP_OFFSET;
                fake_jump->type = INSN_JUMP_UNCONDITIONAL;
                fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
                fake_jump->func = orig_insn->func;
        }

        if (!special_alt->new_len) {
                if (!fake_jump) {
                        WARN("%s: empty alternative at end of section",
                             special_alt->orig_sec->name);
                        return -1;
                }

                *new_insn = fake_jump;
                return 0;
        }

        last_new_insn = NULL;
        alt_group = alt_group_next_index++;
        insn = *new_insn;
        sec_for_each_insn_from(file, insn) {
                if (insn->offset >= special_alt->new_off + special_alt->new_len)
                        break;

                last_new_insn = insn;

                insn->ignore = orig_insn->ignore_alts;
                insn->func = orig_insn->func;
                insn->alt_group = alt_group;

                /*
                 * Since alternative replacement code is copy/pasted by the
                 * kernel after applying relocations, generally such code can't
                 * have relative-address relocation references to outside the
                 * .altinstr_replacement section, unless the arch's
                 * alternatives code can adjust the relative offsets
                 * accordingly.
                 *
                 * The x86 alternatives code adjusts the offsets only when it
                 * encounters a branch instruction at the very beginning of the
                 * replacement group.
                 */
                if ((insn->offset != special_alt->new_off ||
                    (insn->type != INSN_CALL && !is_static_jump(insn))) &&
                    find_reloc_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {

                        WARN_FUNC("unsupported relocation in alternatives section",
                                  insn->sec, insn->offset);
                        return -1;
                }

                if (!is_static_jump(insn))
                        continue;

                if (!insn->immediate)
                        continue;

                dest_off = arch_jump_destination(insn);
                if (dest_off == special_alt->new_off + special_alt->new_len) {
                        if (!fake_jump) {
                                WARN("%s: alternative jump to end of section",
                                     special_alt->orig_sec->name);
                                return -1;
                        }
                        insn->jump_dest = fake_jump;
                }

                if (!insn->jump_dest) {
                        WARN_FUNC("can't find alternative jump destination",
                                  insn->sec, insn->offset);
                        return -1;
                }
        }

        if (!last_new_insn) {
                WARN_FUNC("can't find last new alternative instruction",
                          special_alt->new_sec, special_alt->new_off);
                return -1;
        }

        if (fake_jump)
                list_add(&fake_jump->list, &last_new_insn->list);

        return 0;
}

/*
 * A jump table entry can either convert a nop to a jump or a jump to a nop.
 * If the original instruction is a jump, make the alt entry an effective nop
 * by just skipping the original instruction.
 */
static int handle_jump_alt(struct objtool_file *file,
                           struct special_alt *special_alt,
                           struct instruction *orig_insn,
                           struct instruction **new_insn)
{
        if (orig_insn->type == INSN_NOP)
                return 0;

        if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
                WARN_FUNC("unsupported instruction at jump label",
                          orig_insn->sec, orig_insn->offset);
                return -1;
        }

        *new_insn = list_next_entry(orig_insn, list);
        return 0;
}

/*
 * Read all the special sections which have alternate instructions which can be
 * patched in or redirected to at runtime.  Each instruction having alternate
 * instruction(s) has them added to its insn->alts list, which will be
 * traversed in validate_branch().
 */
static int add_special_section_alts(struct objtool_file *file)
{
        struct list_head special_alts;
        struct instruction *orig_insn, *new_insn;
        struct special_alt *special_alt, *tmp;
        struct alternative *alt;
        int ret;

        ret = special_get_alts(file->elf, &special_alts);
        if (ret)
                return ret;

        list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {

                orig_insn = find_insn(file, special_alt->orig_sec,
                                      special_alt->orig_off);
                if (!orig_insn) {
                        WARN_FUNC("special: can't find orig instruction",
                                  special_alt->orig_sec, special_alt->orig_off);
                        ret = -1;
                        goto out;
                }

                new_insn = NULL;
                if (!special_alt->group || special_alt->new_len) {
                        new_insn = find_insn(file, special_alt->new_sec,
                                             special_alt->new_off);
                        if (!new_insn) {
                                WARN_FUNC("special: can't find new instruction",
                                          special_alt->new_sec,
                                          special_alt->new_off);
                                ret = -1;
                                goto out;
                        }
                }

                if (special_alt->group) {

                        if (!special_alt->orig_len) {
                                WARN_FUNC("empty alternative entry",
                                          orig_insn->sec, orig_insn->offset);
                                continue;
                        }

                        ret = handle_group_alt(file, special_alt, orig_insn,
                                               &new_insn);
                        if (ret)
                                goto out;
                } else if (special_alt->jump_or_nop) {
                        ret = handle_jump_alt(file, special_alt, orig_insn,
                                              &new_insn);
                        if (ret)
                                goto out;
                }

                alt = malloc(sizeof(*alt));
                if (!alt) {
                        WARN("malloc failed");
                        ret = -1;
                        goto out;
                }

                alt->insn = new_insn;
                alt->skip_orig = special_alt->skip_orig;
                orig_insn->ignore_alts |= special_alt->skip_alt;
                list_add_tail(&alt->list, &orig_insn->alts);

                list_del(&special_alt->list);
                free(special_alt);
        }

out:
        return ret;
}

static int add_jump_table(struct objtool_file *file, struct instruction *insn,
                            struct reloc *table)
{
        struct reloc *reloc = table;
        struct instruction *dest_insn;
        struct alternative *alt;
        struct symbol *pfunc = insn->func->pfunc;
        unsigned int prev_offset = 0;

        /*
         * Each @reloc is a switch table relocation which points to the target
         * instruction.
         */
        list_for_each_entry_from(reloc, &table->sec->reloc_list, list) {

                /* Check for the end of the table: */
                if (reloc != table && reloc->jump_table_start)
                        break;

                /* Make sure the table entries are consecutive: */
                if (prev_offset && reloc->offset != prev_offset + 8)
                        break;

                /* Detect function pointers from contiguous objects: */
                if (reloc->sym->sec == pfunc->sec &&
                    reloc->addend == pfunc->offset)
                        break;

                dest_insn = find_insn(file, reloc->sym->sec, reloc->addend);
                if (!dest_insn)
                        break;

                /* Make sure the destination is in the same function: */
                if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
                        break;

                alt = malloc(sizeof(*alt));
                if (!alt) {
                        WARN("malloc failed");
                        return -1;
                }

                alt->insn = dest_insn;
                list_add_tail(&alt->list, &insn->alts);
                prev_offset = reloc->offset;
        }

        if (!prev_offset) {
                WARN_FUNC("can't find switch jump table",
                          insn->sec, insn->offset);
                return -1;
        }

        return 0;
}

/*
 * find_jump_table() - Given a dynamic jump, find the switch jump table in
 * .rodata associated with it.
 *
 * There are 3 basic patterns:
 *
 * 1. jmpq *[rodata addr](,%reg,8)
 *
 *    This is the most common case by far.  It jumps to an address in a simple
 *    jump table which is stored in .rodata.
 *
 * 2. jmpq *[rodata addr](%rip)
 *
 *    This is caused by a rare GCC quirk, currently only seen in three driver
 *    functions in the kernel, only with certain obscure non-distro configs.
 *
 *    As part of an optimization, GCC makes a copy of an existing switch jump
 *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 *    jump) to use a single entry in the table.  The rest of the jump table and
 *    some of its jump targets remain as dead code.
 *
 *    In such a case we can just crudely ignore all unreachable instruction
 *    warnings for the entire object file.  Ideally we would just ignore them
 *    for the function, but that would require redesigning the code quite a
 *    bit.  And honestly that's just not worth doing: unreachable instruction
 *    warnings are of questionable value anyway, and this is such a rare issue.
 *
 * 3. mov [rodata addr],%reg1
 *    ... some instructions ...
 *    jmpq *(%reg1,%reg2,8)
 *
 *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 *
 *    As of GCC 7 there are quite a few more of these and the 'in between' code
 *    is significant. Esp. with KASAN enabled some of the code between the mov
 *    and jmpq uses .rodata itself, which can confuse things.
 *
 *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 *    ensure the same register is used in the mov and jump instructions.
 *
 *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
 */
static struct reloc *find_jump_table(struct objtool_file *file,
                                      struct symbol *func,
                                      struct instruction *insn)
{
        struct reloc *text_reloc, *table_reloc;
        struct instruction *dest_insn, *orig_insn = insn;
        struct section *table_sec;
        unsigned long table_offset;

        /*
         * Backward search using the @first_jump_src links, these help avoid
         * much of the 'in between' code. Which avoids us getting confused by
         * it.
         */
        for (;
             insn && insn->func && insn->func->pfunc == func;
             insn = insn->first_jump_src ?: prev_insn_same_sym(file, insn)) {

                if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
                        break;

                /* allow small jumps within the range */
                if (insn->type == INSN_JUMP_UNCONDITIONAL &&
                    insn->jump_dest &&
                    (insn->jump_dest->offset <= insn->offset ||
                     insn->jump_dest->offset > orig_insn->offset))
                    break;

                /* look for a relocation which references .rodata */
                text_reloc = find_reloc_by_dest_range(file->elf, insn->sec,
                                                    insn->offset, insn->len);
                if (!text_reloc || text_reloc->sym->type != STT_SECTION ||
                    !text_reloc->sym->sec->rodata)
                        continue;

                table_offset = text_reloc->addend;
                table_sec = text_reloc->sym->sec;

                if (text_reloc->type == R_X86_64_PC32)
                        table_offset += 4;

                /*
                 * Make sure the .rodata address isn't associated with a
                 * symbol.  GCC jump tables are anonymous data.
                 *
                 * Also support C jump tables which are in the same format as
                 * switch jump tables.  For objtool to recognize them, they
                 * need to be placed in the C_JUMP_TABLE_SECTION section.  They
                 * have symbols associated with them.
                 */
                if (find_symbol_containing(table_sec, table_offset) &&
                    strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
                        continue;

                /*
                 * Each table entry has a reloc associated with it.  The reloc
                 * should reference text in the same function as the original
                 * instruction.
                 */
                table_reloc = find_reloc_by_dest(file->elf, table_sec, table_offset);
                if (!table_reloc)
                        continue;
                dest_insn = find_insn(file, table_reloc->sym->sec, table_reloc->addend);
                if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
                        continue;

                /*
                 * Use of RIP-relative switch jumps is quite rare, and
                 * indicates a rare GCC quirk/bug which can leave dead code
                 * behind.
                 */
                if (text_reloc->type == R_X86_64_PC32)
                        file->ignore_unreachables = true;

                return table_reloc;
        }

        return NULL;
}

/*
 * First pass: Mark the head of each jump table so that in the next pass,
 * we know when a given jump table ends and the next one starts.
 */
static void mark_func_jump_tables(struct objtool_file *file,
                                    struct symbol *func)
{
        struct instruction *insn, *last = NULL;
        struct reloc *reloc;

        func_for_each_insn(file, func, insn) {
                if (!last)
                        last = insn;

                /*
                 * Store back-pointers for unconditional forward jumps such
                 * that find_jump_table() can back-track using those and
                 * avoid some potentially confusing code.
                 */
                if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
                    insn->offset > last->offset &&
                    insn->jump_dest->offset > insn->offset &&
                    !insn->jump_dest->first_jump_src) {

                        insn->jump_dest->first_jump_src = insn;
                        last = insn->jump_dest;
                }

                if (insn->type != INSN_JUMP_DYNAMIC)
                        continue;

                reloc = find_jump_table(file, func, insn);
                if (reloc) {
                        reloc->jump_table_start = true;
                        insn->jump_table = reloc;
                }
        }
}

static int add_func_jump_tables(struct objtool_file *file,
                                  struct symbol *func)
{
        struct instruction *insn;
        int ret;

        func_for_each_insn(file, func, insn) {
                if (!insn->jump_table)
                        continue;

                ret = add_jump_table(file, insn, insn->jump_table);
                if (ret)
                        return ret;
        }

        return 0;
}

/*
 * For some switch statements, gcc generates a jump table in the .rodata
 * section which contains a list of addresses within the function to jump to.
 * This finds these jump tables and adds them to the insn->alts lists.
 */
static int add_jump_table_alts(struct objtool_file *file)
{
        struct section *sec;
        struct symbol *func;
        int ret;

        if (!file->rodata)
                return 0;

        for_each_sec(file, sec) {
                list_for_each_entry(func, &sec->symbol_list, list) {
                        if (func->type != STT_FUNC)
                                continue;

                        mark_func_jump_tables(file, func);
                        ret = add_func_jump_tables(file, func);
                        if (ret)
                                return ret;
                }
        }

        return 0;
}

static int read_unwind_hints(struct objtool_file *file)
{
        struct section *sec, *relocsec;
        struct reloc *reloc;
        struct unwind_hint *hint;
        struct instruction *insn;
        struct cfi_reg *cfa;
        int i;

        sec = find_section_by_name(file->elf, ".discard.unwind_hints");
        if (!sec)
                return 0;

        relocsec = sec->reloc;
        if (!relocsec) {
                WARN("missing .rela.discard.unwind_hints section");
                return -1;
        }

        if (sec->len % sizeof(struct unwind_hint)) {
                WARN("struct unwind_hint size mismatch");
                return -1;
        }

        file->hints = true;

        for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
                hint = (struct unwind_hint *)sec->data->d_buf + i;

                reloc = find_reloc_by_dest(file->elf, sec, i * sizeof(*hint));
                if (!reloc) {
                        WARN("can't find reloc for unwind_hints[%d]", i);
                        return -1;
                }

                insn = find_insn(file, reloc->sym->sec, reloc->addend);
                if (!insn) {
                        WARN("can't find insn for unwind_hints[%d]", i);
                        return -1;
                }

                cfa = &insn->cfi.cfa;

                if (hint->type == UNWIND_HINT_TYPE_RET_OFFSET) {
                        insn->ret_offset = hint->sp_offset;
                        continue;
                }

                insn->hint = true;

                switch (hint->sp_reg) {
                case ORC_REG_UNDEFINED:
                        cfa->base = CFI_UNDEFINED;
                        break;
                case ORC_REG_SP:
                        cfa->base = CFI_SP;
                        break;
                case ORC_REG_BP:
                        cfa->base = CFI_BP;
                        break;
                case ORC_REG_SP_INDIRECT:
                        cfa->base = CFI_SP_INDIRECT;
                        break;
                case ORC_REG_R10:
                        cfa->base = CFI_R10;
                        break;
                case ORC_REG_R13:
                        cfa->base = CFI_R13;
                        break;
                case ORC_REG_DI:
                        cfa->base = CFI_DI;
                        break;
                case ORC_REG_DX:
                        cfa->base = CFI_DX;
                        break;
                default:
                        WARN_FUNC("unsupported unwind_hint sp base reg %d",
                                  insn->sec, insn->offset, hint->sp_reg);
                        return -1;
                }

                cfa->offset = hint->sp_offset;
                insn->cfi.type = hint->type;
                insn->cfi.end = hint->end;
        }

        return 0;
}

static int read_retpoline_hints(struct objtool_file *file)
{
        struct section *sec;
        struct instruction *insn;
        struct reloc *reloc;

        sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
        if (!sec)
                return 0;

        list_for_each_entry(reloc, &sec->reloc_list, list) {
                if (reloc->sym->type != STT_SECTION) {
                        WARN("unexpected relocation symbol type in %s", sec->name);
                        return -1;
                }

                insn = find_insn(file, reloc->sym->sec, reloc->addend);
                if (!insn) {
                        WARN("bad .discard.retpoline_safe entry");
                        return -1;
                }

                if (insn->type != INSN_JUMP_DYNAMIC &&
                    insn->type != INSN_CALL_DYNAMIC) {
                        WARN_FUNC("retpoline_safe hint not an indirect jump/call",
                                  insn->sec, insn->offset);
                        return -1;
                }

                insn->retpoline_safe = true;
        }

        return 0;
}

static int read_instr_hints(struct objtool_file *file)
{
        struct section *sec;
        struct instruction *insn;
        struct reloc *reloc;

        sec = find_section_by_name(file->elf, ".rela.discard.instr_end");
        if (!sec)
                return 0;

        list_for_each_entry(reloc, &sec->reloc_list, list) {
                if (reloc->sym->type != STT_SECTION) {
                        WARN("unexpected relocation symbol type in %s", sec->name);
                        return -1;
                }

                insn = find_insn(file, reloc->sym->sec, reloc->addend);
                if (!insn) {
                        WARN("bad .discard.instr_end entry");
                        return -1;
                }

                insn->instr--;
        }

        sec = find_section_by_name(file->elf, ".rela.discard.instr_begin");
        if (!sec)
                return 0;

        list_for_each_entry(reloc, &sec->reloc_list, list) {
                if (reloc->sym->type != STT_SECTION) {
                        WARN("unexpected relocation symbol type in %s", sec->name);
                        return -1;
                }

                insn = find_insn(file, reloc->sym->sec, reloc->addend);
                if (!insn) {
                        WARN("bad .discard.instr_begin entry");
                        return -1;
                }

                insn->instr++;
        }

        return 0;
}

static int read_intra_function_calls(struct objtool_file *file)
{
        struct instruction *insn;
        struct section *sec;
        struct reloc *reloc;

        sec = find_section_by_name(file->elf, ".rela.discard.intra_function_calls");
        if (!sec)
                return 0;

        list_for_each_entry(reloc, &sec->reloc_list, list) {
                unsigned long dest_off;

                if (reloc->sym->type != STT_SECTION) {
                        WARN("unexpected relocation symbol type in %s",
                             sec->name);
                        return -1;
                }

                insn = find_insn(file, reloc->sym->sec, reloc->addend);
                if (!insn) {
                        WARN("bad .discard.intra_function_call entry");
                        return -1;
                }

                if (insn->type != INSN_CALL) {
                        WARN_FUNC("intra_function_call not a direct call",
                                  insn->sec, insn->offset);
                        return -1;
                }

                /*
                 * Treat intra-function CALLs as JMPs, but with a stack_op.
                 * See add_call_destinations(), which strips stack_ops from
                 * normal CALLs.
                 */
                insn->type = INSN_JUMP_UNCONDITIONAL;

                dest_off = insn->offset + insn->len + insn->immediate;
                insn->jump_dest = find_insn(file, insn->sec, dest_off);
                if (!insn->jump_dest) {
                        WARN_FUNC("can't find call dest at %s+0x%lx",
                                  insn->sec, insn->offset,
                                  insn->sec->name, dest_off);
                        return -1;
                }
        }

        return 0;
}

static void mark_rodata(struct objtool_file *file)
{
        struct section *sec;
        bool found = false;

        /*
         * Search for the following rodata sections, each of which can
         * potentially contain jump tables:
         *
         * - .rodata: can contain GCC switch tables
         * - .rodata.<func>: same, if -fdata-sections is being used
         * - .rodata..c_jump_table: contains C annotated jump tables
         *
         * .rodata.str1.* sections are ignored; they don't contain jump tables.
         */
        for_each_sec(file, sec) {
                if (!strncmp(sec->name, ".rodata", 7) &&
                    !strstr(sec->name, ".str1.")) {
                        sec->rodata = true;
                        found = true;
                }
        }

        file->rodata = found;
}

static int decode_sections(struct objtool_file *file)
{
        int ret;

        mark_rodata(file);

        ret = decode_instructions(file);
        if (ret)
                return ret;

        ret = add_dead_ends(file);
        if (ret)
                return ret;

        add_ignores(file);
        add_uaccess_safe(file);

        ret = add_ignore_alternatives(file);
        if (ret)
                return ret;

        ret = add_jump_destinations(file);
        if (ret)
                return ret;

        ret = add_special_section_alts(file);
        if (ret)
                return ret;

        ret = read_intra_function_calls(file);
        if (ret)
                return ret;

        ret = add_call_destinations(file);
        if (ret)
                return ret;

        ret = add_jump_table_alts(file);
        if (ret)
                return ret;

        ret = read_unwind_hints(file);
        if (ret)
                return ret;

        ret = read_retpoline_hints(file);
        if (ret)
                return ret;

        ret = read_instr_hints(file);
        if (ret)
                return ret;

        return 0;
}

static bool is_fentry_call(struct instruction *insn)
{
        if (insn->type == INSN_CALL && insn->call_dest &&
            insn->call_dest->type == STT_NOTYPE &&
            !strcmp(insn->call_dest->name, "__fentry__"))
                return true;

        return false;
}

static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state)
{
        u8 ret_offset = insn->ret_offset;
        struct cfi_state *cfi = &state->cfi;
        int i;

        if (cfi->cfa.base != initial_func_cfi.cfa.base || cfi->drap)
                return true;

        if (cfi->cfa.offset != initial_func_cfi.cfa.offset + ret_offset)
                return true;

        if (cfi->stack_size != initial_func_cfi.cfa.offset + ret_offset)
                return true;

        /*
         * If there is a ret offset hint then don't check registers
         * because a callee-saved register might have been pushed on
         * the stack.
         */
        if (ret_offset)
                return false;

        for (i = 0; i < CFI_NUM_REGS; i++) {
                if (cfi->regs[i].base != initial_func_cfi.regs[i].base ||
                    cfi->regs[i].offset != initial_func_cfi.regs[i].offset)
                        return true;
        }

        return false;
}

static bool has_valid_stack_frame(struct insn_state *state)
{
        struct cfi_state *cfi = &state->cfi;

        if (cfi->cfa.base == CFI_BP && cfi->regs[CFI_BP].base == CFI_CFA &&
            cfi->regs[CFI_BP].offset == -16)
                return true;

        if (cfi->drap && cfi->regs[CFI_BP].base == CFI_BP)
                return true;

        return false;
}

static int update_cfi_state_regs(struct instruction *insn,
                                  struct cfi_state *cfi,
                                  struct stack_op *op)
{
        struct cfi_reg *cfa = &cfi->cfa;

        if (cfa->base != CFI_SP && cfa->base != CFI_SP_INDIRECT)
                return 0;

        /* push */
        if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
                cfa->offset += 8;

        /* pop */
        if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
                cfa->offset -= 8;

        /* add immediate to sp */
        if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
            op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
                cfa->offset -= op->src.offset;

        return 0;
}

static void save_reg(struct cfi_state *cfi, unsigned char reg, int base, int offset)
{
        if (arch_callee_saved_reg(reg) &&
            cfi->regs[reg].base == CFI_UNDEFINED) {
                cfi->regs[reg].base = base;
                cfi->regs[reg].offset = offset;
        }
}

static void restore_reg(struct cfi_state *cfi, unsigned char reg)
{
        cfi->regs[reg].base = initial_func_cfi.regs[reg].base;
        cfi->regs[reg].offset = initial_func_cfi.regs[reg].offset;
}

/*
 * A note about DRAP stack alignment:
 *
 * GCC has the concept of a DRAP register, which is used to help keep track of
 * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
 * register.  The typical DRAP pattern is:
 *
 *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
 *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
 *   41 ff 72 f8                pushq  -0x8(%r10)
 *   55                         push   %rbp
 *   48 89 e5                   mov    %rsp,%rbp
 *                              (more pushes)
 *   41 52                      push   %r10
 *                              ...
 *   41 5a                      pop    %r10
 *                              (more pops)
 *   5d                         pop    %rbp
 *   49 8d 62 f8                lea    -0x8(%r10),%rsp
 *   c3                         retq
 *
 * There are some variations in the epilogues, like:
 *
 *   5b                         pop    %rbx
 *   41 5a                      pop    %r10
 *   41 5c                      pop    %r12
 *   41 5d                      pop    %r13
 *   41 5e                      pop    %r14
 *   c9                         leaveq
 *   49 8d 62 f8                lea    -0x8(%r10),%rsp
 *   c3                         retq
 *
 * and:
 *
 *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
 *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
 *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
 *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
 *   c9                         leaveq
 *   49 8d 62 f8                lea    -0x8(%r10),%rsp
 *   c3                         retq
 *
 * Sometimes r13 is used as the DRAP register, in which case it's saved and
 * restored beforehand:
 *
 *   41 55                      push   %r13
 *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
 *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
 *                              ...
 *   49 8d 65 f0                lea    -0x10(%r13),%rsp
 *   41 5d                      pop    %r13
 *   c3                         retq
 */
static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
                             struct stack_op *op)
{
        struct cfi_reg *cfa = &cfi->cfa;
        struct cfi_reg *regs = cfi->regs;

        /* stack operations don't make sense with an undefined CFA */
        if (cfa->base == CFI_UNDEFINED) {
                if (insn->func) {
                        WARN_FUNC("undefined stack state", insn->sec, insn->offset);
                        return -1;
                }
                return 0;
        }

        if (cfi->type == ORC_TYPE_REGS || cfi->type == ORC_TYPE_REGS_IRET)
                return update_cfi_state_regs(insn, cfi, op);

        switch (op->dest.type) {

        case OP_DEST_REG:
                switch (op->src.type) {

                case OP_SRC_REG:
                        if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
                            cfa->base == CFI_SP &&
                            regs[CFI_BP].base == CFI_CFA &&
                            regs[CFI_BP].offset == -cfa->offset) {

                                /* mov %rsp, %rbp */
                                cfa->base = op->dest.reg;
                                cfi->bp_scratch = false;
                        }

                        else if (op->src.reg == CFI_SP &&
                                 op->dest.reg == CFI_BP && cfi->drap) {

                                /* drap: mov %rsp, %rbp */
                                regs[CFI_BP].base = CFI_BP;
                                regs[CFI_BP].offset = -cfi->stack_size;
                                cfi->bp_scratch = false;
                        }

                        else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {

                                /*
                                 * mov %rsp, %reg
                                 *
                                 * This is needed for the rare case where GCC
                                 * does:
                                 *
                                 *   mov    %rsp, %rax
                                 *   ...
                                 *   mov    %rax, %rsp
                                 */
                                cfi->vals[op->dest.reg].base = CFI_CFA;
                                cfi->vals[op->dest.reg].offset = -cfi->stack_size;
                        }

                        else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
                                 cfa->base == CFI_BP) {

                                /*
                                 * mov %rbp, %rsp
                                 *
                                 * Restore the original stack pointer (Clang).
                                 */
                                cfi->stack_size = -cfi->regs[CFI_BP].offset;
                        }

                        else if (op->dest.reg == cfa->base) {

                                /* mov %reg, %rsp */
                                if (cfa->base == CFI_SP &&
                                    cfi->vals[op->src.reg].base == CFI_CFA) {

                                        /*
                                         * This is needed for the rare case
                                         * where GCC does something dumb like:
                                         *
                                         *   lea    0x8(%rsp), %rcx
                                         *   ...
                                         *   mov    %rcx, %rsp
                                         */
                                        cfa->offset = -cfi->vals[op->src.reg].offset;
                                        cfi->stack_size = cfa->offset;

                                } else {
                                        cfa->base = CFI_UNDEFINED;
                                        cfa->offset = 0;
                                }
                        }

                        break;

                case OP_SRC_ADD:
                        if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {

                                /* add imm, %rsp */
                                cfi->stack_size -= op->src.offset;
                                if (cfa->base == CFI_SP)
                                        cfa->offset -= op->src.offset;
                                break;
                        }

                        if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {

                                /* lea disp(%rbp), %rsp */
                                cfi->stack_size = -(op->src.offset + regs[CFI_BP].offset);
                                break;
                        }

                        if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {

                                /* drap: lea disp(%rsp), %drap */
                                cfi->drap_reg = op->dest.reg;

                                /*
                                 * lea disp(%rsp), %reg
                                 *
                                 * This is needed for the rare case where GCC
                                 * does something dumb like:
                                 *
                                 *   lea    0x8(%rsp), %rcx
                                 *   ...
                                 *   mov    %rcx, %rsp
                                 */
                                cfi->vals[op->dest.reg].base = CFI_CFA;
                                cfi->vals[op->dest.reg].offset = \
                                        -cfi->stack_size + op->src.offset;

                                break;
                        }

                        if (cfi->drap && op->dest.reg == CFI_SP &&
                            op->src.reg == cfi->drap_reg) {

                                 /* drap: lea disp(%drap), %rsp */
                                cfa->base = CFI_SP;
                                cfa->offset = cfi->stack_size = -op->src.offset;
                                cfi->drap_reg = CFI_UNDEFINED;
                                cfi->drap = false;
                                break;
                        }

                        if (op->dest.reg == cfi->cfa.base) {
                                WARN_FUNC("unsupported stack register modification",
                                          insn->sec, insn->offset);
                                return -1;
                        }

                        break;

                case OP_SRC_AND:
                        if (op->dest.reg != CFI_SP ||
                            (cfi->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
                            (cfi->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
                                WARN_FUNC("unsupported stack pointer realignment",
                                          insn->sec, insn->offset);
                                return -1;
                        }

                        if (cfi->drap_reg != CFI_UNDEFINED) {
                                /* drap: and imm, %rsp */
                                cfa->base = cfi->drap_reg;
                                cfa->offset = cfi->stack_size = 0;
                                cfi->drap = true;
                        }

                        /*
                         * Older versions of GCC (4.8ish) realign the stack
                         * without DRAP, with a frame pointer.
                         */

                        break;

                case OP_SRC_POP:
                case OP_SRC_POPF:
                        if (!cfi->drap && op->dest.reg == cfa->base) {

                                /* pop %rbp */
                                cfa->base = CFI_SP;
                        }

                        if (cfi->drap && cfa->base == CFI_BP_INDIRECT &&
                            op->dest.reg == cfi->drap_reg &&
                            cfi->drap_offset == -cfi->stack_size) {

                                /* drap: pop %drap */
                                cfa->base = cfi->drap_reg;
                                cfa->offset = 0;
                                cfi->drap_offset = -1;

                        } else if (regs[op->dest.reg].offset == -cfi->stack_size) {

                                /* pop %reg */
                                restore_reg(cfi, op->dest.reg);
                        }

                        cfi->stack_size -= 8;
                        if (cfa->base == CFI_SP)
                                cfa->offset -= 8;

                        break;

                case OP_SRC_REG_INDIRECT:
                        if (cfi->drap && op->src.reg == CFI_BP &&
                            op->src.offset == cfi->drap_offset) {

                                /* drap: mov disp(%rbp), %drap */
                                cfa->base = cfi->drap_reg;
                                cfa->offset = 0;
                                cfi->drap_offset = -1;
                        }

                        if (cfi->drap && op->src.reg == CFI_BP &&
                            op->src.offset == regs[op->dest.reg].offset) {

                                /* drap: mov disp(%rbp), %reg */
                                restore_reg(cfi, op->dest.reg);

                        } else if (op->src.reg == cfa->base &&
                            op->src.offset == regs[op->dest.reg].offset + cfa->offset) {

                                /* mov disp(%rbp), %reg */
                                /* mov disp(%rsp), %reg */
                                restore_reg(cfi, op->dest.reg);
                        }

                        break;

                default:
                        WARN_FUNC("unknown stack-related instruction",
                                  insn->sec, insn->offset);
                        return -1;
                }

                break;

        case OP_DEST_PUSH:
        case OP_DEST_PUSHF:
                cfi->stack_size += 8;
                if (cfa->base == CFI_SP)
                        cfa->offset += 8;

                if (op->src.type != OP_SRC_REG)
                        break;

                if (cfi->drap) {
                        if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {

                                /* drap: push %drap */
                                cfa->base = CFI_BP_INDIRECT;
                                cfa->offset = -cfi->stack_size;

                                /* save drap so we know when to restore it */
                                cfi->drap_offset = -cfi->stack_size;

                        } else if (op->src.reg == CFI_BP && cfa->base == cfi->drap_reg) {

                                /* drap: push %rbp */
                                cfi->stack_size = 0;

                        } else if (regs[op->src.reg].base == CFI_UNDEFINED) {

                                /* drap: push %reg */
                                save_reg(cfi, op->src.reg, CFI_BP, -cfi->stack_size);
                        }

                } else {

                        /* push %reg */
                        save_reg(cfi, op->src.reg, CFI_CFA, -cfi->stack_size);
                }

                /* detect when asm code uses rbp as a scratch register */
                if (!no_fp && insn->func && op->src.reg == CFI_BP &&
                    cfa->base != CFI_BP)
                        cfi->bp_scratch = true;
                break;

        case OP_DEST_REG_INDIRECT:

                if (cfi->drap) {
                        if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {

                                /* drap: mov %drap, disp(%rbp) */
                                cfa->base = CFI_BP_INDIRECT;
                                cfa->offset = op->dest.offset;

                                /* save drap offset so we know when to restore it */
                                cfi->drap_offset = op->dest.offset;
                        }

                        else if (regs[op->src.reg].base == CFI_UNDEFINED) {

                                /* drap: mov reg, disp(%rbp) */
                                save_reg(cfi, op->src.reg, CFI_BP, op->dest.offset);
                        }

                } else if (op->dest.reg == cfa->base) {

                        /* mov reg, disp(%rbp) */
                        /* mov reg, disp(%rsp) */
                        save_reg(cfi, op->src.reg, CFI_CFA,
                                 op->dest.offset - cfi->cfa.offset);
                }

                break;

        case OP_DEST_LEAVE:
                if ((!cfi->drap && cfa->base != CFI_BP) ||
                    (cfi->drap && cfa->base != cfi->drap_reg)) {
                        WARN_FUNC("leave instruction with modified stack frame",
                                  insn->sec, insn->offset);
                        return -1;
                }

                /* leave (mov %rbp, %rsp; pop %rbp) */

                cfi->stack_size = -cfi->regs[CFI_BP].offset - 8;
                restore_reg(cfi, CFI_BP);

                if (!cfi->drap) {
                        cfa->base = CFI_SP;
                        cfa->offset -= 8;
                }

                break;

        case OP_DEST_MEM:
                if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
                        WARN_FUNC("unknown stack-related memory operation",
                                  insn->sec, insn->offset);
                        return -1;
                }

                /* pop mem */
                cfi->stack_size -= 8;
                if (cfa->base == CFI_SP)
                        cfa->offset -= 8;

                break;

        default:
                WARN_FUNC("unknown stack-related instruction",
                          insn->sec, insn->offset);
                return -1;
        }

        return 0;
}

static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
{
        struct stack_op *op;

        list_for_each_entry(op, &insn->stack_ops, list) {
                struct cfi_state old_cfi = state->cfi;
                int res;

                res = update_cfi_state(insn, &state->cfi, op);
                if (res)
                        return res;

                if (insn->alt_group && memcmp(&state->cfi, &old_cfi, sizeof(struct cfi_state))) {
                        WARN_FUNC("alternative modifies stack", insn->sec, insn->offset);
                        return -1;
                }

                if (op->dest.type == OP_DEST_PUSHF) {
                        if (!state->uaccess_stack) {
                                state->uaccess_stack = 1;
                        } else if (state->uaccess_stack >> 31) {
                                WARN_FUNC("PUSHF stack exhausted",
                                          insn->sec, insn->offset);
                                return 1;
                        }
                        state->uaccess_stack <<= 1;
                        state->uaccess_stack  |= state->uaccess;
                }

                if (op->src.type == OP_SRC_POPF) {
                        if (state->uaccess_stack) {
                                state->uaccess = state->uaccess_stack & 1;
                                state->uaccess_stack >>= 1;
                                if (state->uaccess_stack == 1)
                                        state->uaccess_stack = 0;
                        }
                }
        }

        return 0;
}

static bool insn_cfi_match(struct instruction *insn, struct cfi_state *cfi2)
{
        struct cfi_state *cfi1 = &insn->cfi;
        int i;

        if (memcmp(&cfi1->cfa, &cfi2->cfa, sizeof(cfi1->cfa))) {

                WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
                          insn->sec, insn->offset,
                          cfi1->cfa.base, cfi1->cfa.offset,
                          cfi2->cfa.base, cfi2->cfa.offset);

        } else if (memcmp(&cfi1->regs, &cfi2->regs, sizeof(cfi1->regs))) {
                for (i = 0; i < CFI_NUM_REGS; i++) {
                        if (!memcmp(&cfi1->regs[i], &cfi2->regs[i],
                                    sizeof(struct cfi_reg)))
                                continue;

                        WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
                                  insn->sec, insn->offset,
                                  i, cfi1->regs[i].base, cfi1->regs[i].offset,
                                  i, cfi2->regs[i].base, cfi2->regs[i].offset);
                        break;
                }

        } else if (cfi1->type != cfi2->type) {

                WARN_FUNC("stack state mismatch: type1=%d type2=%d",
                          insn->sec, insn->offset, cfi1->type, cfi2->type);

        } else if (cfi1->drap != cfi2->drap ||
                   (cfi1->drap && cfi1->drap_reg != cfi2->drap_reg) ||
                   (cfi1->drap && cfi1->drap_offset != cfi2->drap_offset)) {

                WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
                          insn->sec, insn->offset,
                          cfi1->drap, cfi1->drap_reg, cfi1->drap_offset,
                          cfi2->drap, cfi2->drap_reg, cfi2->drap_offset);

        } else
                return true;

        return false;
}

static inline bool func_uaccess_safe(struct symbol *func)
{
        if (func)
                return func->uaccess_safe;

        return false;
}

static inline const char *call_dest_name(struct instruction *insn)
{
        if (insn->call_dest)
                return insn->call_dest->name;

        return "{dynamic}";
}

static inline bool noinstr_call_dest(struct symbol *func)
{
        /*
         * We can't deal with indirect function calls at present;
         * assume they're instrumented.
         */
        if (!func)
                return false;

        /*
         * If the symbol is from a noinstr section; we good.
         */
        if (func->sec->noinstr)
                return true;

        /*
         * The __ubsan_handle_*() calls are like WARN(), they only happen when
         * something 'BAD' happened. At the risk of taking the machine down,
         * let them proceed to get the message out.
         */
        if (!strncmp(func->name, "__ubsan_handle_", 15))
                return true;

        return false;
}

static int validate_call(struct instruction *insn, struct insn_state *state)
{
        if (state->noinstr && state->instr <= 0 &&
            !noinstr_call_dest(insn->call_dest)) {
                WARN_FUNC("call to %s() leaves .noinstr.text section",
                                insn->sec, insn->offset, call_dest_name(insn));
                return 1;
        }

        if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
                WARN_FUNC("call to %s() with UACCESS enabled",
                                insn->sec, insn->offset, call_dest_name(insn));
                return 1;
        }

        if (state->df) {
                WARN_FUNC("call to %s() with DF set",
                                insn->sec, insn->offset, call_dest_name(insn));
                return 1;
        }

        return 0;
}

static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
{
        if (has_modified_stack_frame(insn, state)) {
                WARN_FUNC("sibling call from callable instruction with modified stack frame",
                                insn->sec, insn->offset);
                return 1;
        }

        return validate_call(insn, state);
}

static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
{
        if (state->noinstr && state->instr > 0) {
                WARN_FUNC("return with instrumentation enabled",
                          insn->sec, insn->offset);
                return 1;
        }

        if (state->uaccess && !func_uaccess_safe(func)) {
                WARN_FUNC("return with UACCESS enabled",
                          insn->sec, insn->offset);
                return 1;
        }

        if (!state->uaccess && func_uaccess_safe(func)) {
                WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
                          insn->sec, insn->offset);
                return 1;
        }

        if (state->df) {
                WARN_FUNC("return with DF set",
                          insn->sec, insn->offset);
                return 1;
        }

        if (func && has_modified_stack_frame(insn, state)) {
                WARN_FUNC("return with modified stack frame",
                          insn->sec, insn->offset);
                return 1;
        }

        if (state->cfi.bp_scratch) {
                WARN_FUNC("BP used as a scratch register",
                          insn->sec, insn->offset);
                return 1;
        }

        return 0;
}

/*
 * Alternatives should not contain any ORC entries, this in turn means they
 * should not contain any CFI ops, which implies all instructions should have
 * the same same CFI state.
 *
 * It is possible to constuct alternatives that have unreachable holes that go
 * unreported (because they're NOPs), such holes would result in CFI_UNDEFINED
 * states which then results in ORC entries, which we just said we didn't want.
 *
 * Avoid them by copying the CFI entry of the first instruction into the whole
 * alternative.
 */
static void fill_alternative_cfi(struct objtool_file *file, struct instruction *insn)
{
        struct instruction *first_insn = insn;
        int alt_group = insn->alt_group;

        sec_for_each_insn_continue(file, insn) {
                if (insn->alt_group != alt_group)
                        break;
                insn->cfi = first_insn->cfi;
        }
}

/*
 * Follow the branch starting at the given instruction, and recursively follow
 * any other branches (jumps).  Meanwhile, track the frame pointer state at
 * each instruction and validate all the rules described in
 * tools/objtool/Documentation/stack-validation.txt.
 */
static int validate_branch(struct objtool_file *file, struct symbol *func,
                           struct instruction *insn, struct insn_state state)
{
        struct alternative *alt;
        struct instruction *next_insn;
        struct section *sec;
        u8 visited;
        int ret;

        sec = insn->sec;

        while (1) {
                next_insn = next_insn_same_sec(file, insn);

                if (file->c_file && func && insn->func && func != insn->func->pfunc) {
                        WARN("%s() falls through to next function %s()",
                             func->name, insn->func->name);
                        return 1;
                }

                if (func && insn->ignore) {
                        WARN_FUNC("BUG: why am I validating an ignored function?",
                                  sec, insn->offset);
                        return 1;
                }

                visited = 1 << state.uaccess;
                if (insn->visited) {
                        if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
                                return 1;

                        if (insn->visited & visited)
                                return 0;
                }

                if (state.noinstr)
                        state.instr += insn->instr;

                if (insn->hint)
                        state.cfi = insn->cfi;
                else
                        insn->cfi = state.cfi;

                insn->visited |= visited;

                if (!insn->ignore_alts && !list_empty(&insn->alts)) {
                        bool skip_orig = false;

                        list_for_each_entry(alt, &insn->alts, list) {
                                if (alt->skip_orig)
                                        skip_orig = true;

                                ret = validate_branch(file, func, alt->insn, state);
                                if (ret) {
                                        if (backtrace)
                                                BT_FUNC("(alt)", insn);
                                        return ret;
                                }
                        }

                        if (insn->alt_group)
                                fill_alternative_cfi(file, insn);

                        if (skip_orig)
                                return 0;
                }

                if (handle_insn_ops(insn, &state))
                        return 1;

                switch (insn->type) {

                case INSN_RETURN:
                        return validate_return(func, insn, &state);

                case INSN_CALL:
                case INSN_CALL_DYNAMIC:
                        ret = validate_call(insn, &state);
                        if (ret)
                                return ret;

                        if (!no_fp && func && !is_fentry_call(insn) &&
                            !has_valid_stack_frame(&state)) {
                                WARN_FUNC("call without frame pointer save/setup",
                                          sec, insn->offset);
                                return 1;
                        }

                        if (dead_end_function(file, insn->call_dest))
                                return 0;

                        break;

                case INSN_JUMP_CONDITIONAL:
                case INSN_JUMP_UNCONDITIONAL:
                        if (func && is_sibling_call(insn)) {
                                ret = validate_sibling_call(insn, &state);
                                if (ret)
                                        return ret;

                        } else if (insn->jump_dest) {
                                ret = validate_branch(file, func,
                                                      insn->jump_dest, state);
                                if (ret) {
                                        if (backtrace)
                                                BT_FUNC("(branch)", insn);
                                        return ret;
                                }
                        }

                        if (insn->type == INSN_JUMP_UNCONDITIONAL)
                                return 0;

                        break;

                case INSN_JUMP_DYNAMIC:
                case INSN_JUMP_DYNAMIC_CONDITIONAL:
                        if (func && is_sibling_call(insn)) {
                                ret = validate_sibling_call(insn, &state);
                                if (ret)
                                        return ret;
                        }

                        if (insn->type == INSN_JUMP_DYNAMIC)
                                return 0;

                        break;

                case INSN_CONTEXT_SWITCH:
                        if (func && (!next_insn || !next_insn->hint)) {
                                WARN_FUNC("unsupported instruction in callable function",
                                          sec, insn->offset);
                                return 1;
                        }
                        return 0;

                case INSN_STAC:
                        if (state.uaccess) {
                                WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
                                return 1;
                        }

                        state.uaccess = true;
                        break;

                case INSN_CLAC:
                        if (!state.uaccess && func) {
                                WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
                                return 1;
                        }

                        if (func_uaccess_safe(func) && !state.uaccess_stack) {
                                WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
                                return 1;
                        }

                        state.uaccess = false;
                        break;

                case INSN_STD:
                        if (state.df)
                                WARN_FUNC("recursive STD", sec, insn->offset);

                        state.df = true;
                        break;

                case INSN_CLD:
                        if (!state.df && func)
                                WARN_FUNC("redundant CLD", sec, insn->offset);

                        state.df = false;
                        break;

                default:
                        break;
                }

                if (insn->dead_end)
                        return 0;

                if (!next_insn) {
                        if (state.cfi.cfa.base == CFI_UNDEFINED)
                                return 0;
                        WARN("%s: unexpected end of section", sec->name);
                        return 1;
                }

                insn = next_insn;
        }

        return 0;
}

static int validate_unwind_hints(struct objtool_file *file, struct section *sec)
{
        struct instruction *insn;
        struct insn_state state;
        int ret, warnings = 0;

        if (!file->hints)
                return 0;

        init_insn_state(&state, sec);

        if (sec) {
                insn = find_insn(file, sec, 0);
                if (!insn)
                        return 0;
        } else {
                insn = list_first_entry(&file->insn_list, typeof(*insn), list);
        }

        while (&insn->list != &file->insn_list && (!sec || insn->sec == sec)) {
                if (insn->hint && !insn->visited) {
                        ret = validate_branch(file, insn->func, insn, state);
                        if (ret && backtrace)
                                BT_FUNC("<=== (hint)", insn);
                        warnings += ret;
                }

                insn = list_next_entry(insn, list);
        }

        return warnings;
}

static int validate_retpoline(struct objtool_file *file)
{
        struct instruction *insn;
        int warnings = 0;

        for_each_insn(file, insn) {
                if (insn->type != INSN_JUMP_DYNAMIC &&
                    insn->type != INSN_CALL_DYNAMIC)
                        continue;

                if (insn->retpoline_safe)
                        continue;

                /*
                 * .init.text code is ran before userspace and thus doesn't
                 * strictly need retpolines, except for modules which are
                 * loaded late, they very much do need retpoline in their
                 * .init.text
                 */
                if (!strcmp(insn->sec->name, ".init.text") && !module)
                        continue;

                WARN_FUNC("indirect %s found in RETPOLINE build",
                          insn->sec, insn->offset,
                          insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");

                warnings++;
        }

        return warnings;
}

static bool is_kasan_insn(struct instruction *insn)
{
        return (insn->type == INSN_CALL &&
                !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
}

static bool is_ubsan_insn(struct instruction *insn)
{
        return (insn->type == INSN_CALL &&
                !strcmp(insn->call_dest->name,
                        "__ubsan_handle_builtin_unreachable"));
}

static bool ignore_unreachable_insn(struct instruction *insn)
{
        int i;

        if (insn->ignore || insn->type == INSN_NOP)
                return true;

        /*
         * Ignore any unused exceptions.  This can happen when a whitelisted
         * function has an exception table entry.
         *
         * Also ignore alternative replacement instructions.  This can happen
         * when a whitelisted function uses one of the ALTERNATIVE macros.
         */
        if (!strcmp(insn->sec->name, ".fixup") ||
            !strcmp(insn->sec->name, ".altinstr_replacement") ||
            !strcmp(insn->sec->name, ".altinstr_aux"))
                return true;

        if (!insn->func)
                return false;

        /*
         * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
         * __builtin_unreachable().  The BUG() macro has an unreachable() after
         * the UD2, which causes GCC's undefined trap logic to emit another UD2
         * (or occasionally a JMP to UD2).
         */
        if (list_prev_entry(insn, list)->dead_end &&
            (insn->type == INSN_BUG ||
             (insn->type == INSN_JUMP_UNCONDITIONAL &&
              insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
                return true;

        /*
         * Check if this (or a subsequent) instruction is related to
         * CONFIG_UBSAN or CONFIG_KASAN.
         *
         * End the search at 5 instructions to avoid going into the weeds.
         */
        for (i = 0; i < 5; i++) {

                if (is_kasan_insn(insn) || is_ubsan_insn(insn))
                        return true;

                if (insn->type == INSN_JUMP_UNCONDITIONAL) {
                        if (insn->jump_dest &&
                            insn->jump_dest->func == insn->func) {
                                insn = insn->jump_dest;
                                continue;
                        }

                        break;
                }

                if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
                        break;

                insn = list_next_entry(insn, list);
        }

        return false;
}

static int validate_symbol(struct objtool_file *file, struct section *sec,
                           struct symbol *sym, struct insn_state *state)
{
        struct instruction *insn;
        int ret;

        if (!sym->len) {
                WARN("%s() is missing an ELF size annotation", sym->name);
                return 1;
        }

        if (sym->pfunc != sym || sym->alias != sym)
                return 0;

        insn = find_insn(file, sec, sym->offset);
        if (!insn || insn->ignore || insn->visited)
                return 0;

        state->uaccess = sym->uaccess_safe;

        ret = validate_branch(file, insn->func, insn, *state);
        if (ret && backtrace)
                BT_FUNC("<=== (sym)", insn);
        return ret;
}

static int validate_section(struct objtool_file *file, struct section *sec)
{
        struct insn_state state;
        struct symbol *func;
        int warnings = 0;

        list_for_each_entry(func, &sec->symbol_list, list) {
                if (func->type != STT_FUNC)
                        continue;

                init_insn_state(&state, sec);
                state.cfi.cfa = initial_func_cfi.cfa;
                memcpy(&state.cfi.regs, &initial_func_cfi.regs,
                       CFI_NUM_REGS * sizeof(struct cfi_reg));
                state.cfi.stack_size = initial_func_cfi.cfa.offset;

                warnings += validate_symbol(file, sec, func, &state);
        }

        return warnings;
}

static int validate_vmlinux_functions(struct objtool_file *file)
{
        struct section *sec;
        int warnings = 0;

        sec = find_section_by_name(file->elf, ".noinstr.text");
        if (sec) {
                warnings += validate_section(file, sec);
                warnings += validate_unwind_hints(file, sec);
        }

        sec = find_section_by_name(file->elf, ".entry.text");
        if (sec) {
                warnings += validate_section(file, sec);
                warnings += validate_unwind_hints(file, sec);
        }

        return warnings;
}

static int validate_functions(struct objtool_file *file)
{
        struct section *sec;
        int warnings = 0;

        for_each_sec(file, sec) {
                if (!(sec->sh.sh_flags & SHF_EXECINSTR))
                        continue;

                warnings += validate_section(file, sec);
        }

        return warnings;
}

static int validate_reachable_instructions(struct objtool_file *file)
{
        struct instruction *insn;

        if (file->ignore_unreachables)
                return 0;

        for_each_insn(file, insn) {
                if (insn->visited || ignore_unreachable_insn(insn))
                        continue;

                WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
                return 1;
        }

        return 0;
}

static struct objtool_file file;

int check(const char *_objname, bool orc)
{
        int ret, warnings = 0;

        objname = _objname;

        file.elf = elf_open_read(objname, O_RDWR);
        if (!file.elf)
                return 1;

        INIT_LIST_HEAD(&file.insn_list);
        hash_init(file.insn_hash);
        file.c_file = !vmlinux && find_section_by_name(file.elf, ".comment");
        file.ignore_unreachables = no_unreachable;
        file.hints = false;

        arch_initial_func_cfi_state(&initial_func_cfi);

        ret = decode_sections(&file);
        if (ret < 0)
                goto out;
        warnings += ret;

        if (list_empty(&file.insn_list))
                goto out;

        if (vmlinux && !validate_dup) {
                ret = validate_vmlinux_functions(&file);
                if (ret < 0)
                        goto out;

                warnings += ret;
                goto out;
        }

        if (retpoline) {
                ret = validate_retpoline(&file);
                if (ret < 0)
                        return ret;
                warnings += ret;
        }

        ret = validate_functions(&file);
        if (ret < 0)
                goto out;
        warnings += ret;

        ret = validate_unwind_hints(&file, NULL);
        if (ret < 0)
                goto out;
        warnings += ret;

        if (!warnings) {
                ret = validate_reachable_instructions(&file);
                if (ret < 0)
                        goto out;
                warnings += ret;
        }

        if (orc) {
                ret = create_orc(&file);
                if (ret < 0)
                        goto out;

                ret = create_orc_sections(&file);
                if (ret < 0)
                        goto out;
        }

        if (file.elf->changed) {
                ret = elf_write(file.elf);
                if (ret < 0)
                        goto out;
        }

out:
        if (ret < 0) {
                /*
                 *  Fatal error.  The binary is corrupt or otherwise broken in
                 *  some way, or objtool itself is broken.  Fail the kernel
                 *  build.
                 */
                return ret;
        }

        return 0;
}